Conduction-Cooled Accelerated Test Fixture

ABSTRACT

According to one embodiment of the invention, a testing apparatus for executing highly accelerated life testing on at least one test subject includes at least one structure operable to thermally stress the test subject via conduction and at least one pneumatic hammer operable to input imparting vibrations to the test subject. According to another embodiment of the invention, a method for executing highly accelerated life testing of at least one test subject includes applying a thermal stress to the test subject via conduction at a rate of change of at least 8° C. per minute and imparting vibrations to the test subject at a rate of at least 3Gs rms.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to the field of highly-accelerated lifetesting (HALT) fixtures and, more particularly, to a conduction-cooledaccelerated test fixture.

BACKGROUND OF THE INVENTION

It is important for a manufacturer to test its products before releasingthem to the public to ensure that the products function reliably whenreleased. Faulty or dysfunctional products can often cause consumerconfidence in the manufacturer to decrease, and in addition, can havecostly repercussions for the manufacturer consisting of, among otherthings, product recalls, product liability suits, and the like. However,thorough testing of consumer products can be realized through the use ofHALT fixtures.

HALT fixtures are designed to test products to uncover design defectsand weaknesses in electronic and electromechanical assemblies byapplying extreme vibrational and thermal stresses to the product. Thethermal stresses can consist of rapid and extreme temperature changes.Through the application of such stresses to a product during HALTtesting, the HALT fixture can emulate in a brief time frame (i.e., a fewdays or hours) the entire lifetime of stresses that a product willtypically undergo during conventional use.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, a testing apparatus forexecuting highly accelerated life testing on at least one test subjectincludes at least one structure operable to thermally stress the testsubject via conduction and at least one pneumatic hammer operable toinput imparting vibrations to the test subject. According to anotherembodiment of the invention, a method for executing highly acceleratedlife testing of at least one test subject includes applying a thermalstress to the test subject via conduction at a rate of change of atleast 8° C. per minute and imparting vibrations to the test subject at arate of at least 3Gs rms.

Certain embodiments of the invention may provide numerous technicaladvantages. For example, a technical advantage of one embodiment mayinclude the reduction of overlooked design flaws or weaknesses, whichreduction results from more accurate emulation of the test subject'sthermal environment during HALT testing. An additional technicaladvantage of this embodiment and/or of an alternate embodiment mayinclude chamber-free HALT testing.

Although specific advantages have been enumerated above, variousembodiments may include all, some, or none of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the following figuresand description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the presentinvention and its advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic diagram of an example embodiment of a testingapparatus housed inside of a chamber;

FIG. 2 is an illustration of the testing apparatus of FIG. 1;

FIG. 3A is an illustration of the inner face of a rail of the testingapparatus of FIG. 1;

FIG. 3B is an illustration of an alternate view of the inner face of therail of FIG. 3A;

FIG. 3C is a schematic diagram of a vertical cross-section of the shortside of the rail of FIG. 3A; and

FIG. 3D is a schematic diagram of a vertical cross-section of the longside of the rail of FIG. 3A.

DETAILED DESCRIPTION

It should be understood at the outset that although example embodimentsof the present invention are illustrated below, the present inventionmay be implemented using any number of techniques, whether currentlyknown or in existence. The present invention should in no way be limitedto the example embodiments, drawings, and techniques illustrated below,including the embodiments and implementation illustrated and describedherein. Additionally, the drawings are not necessarily drawn to scale.

FIG. 1 is a schematic diagram of an example embodiment of a testingapparatus 100 housed inside of a chamber 184. The testing apparatus 100is operable to stress a test subject 120 by applying either or both of athermal stress and vibrational stress to the test subject 120. The testsubject 120 can include one or more electrical circuit cards or otherelectrical components. In one example implementation, the test subject120 is a circuit card that contains a protective cover; however, testconfiguration apparatus 100 may be used with a variety of types of testsubjects.

The testing apparatus 100 includes, in this embodiment, a pair ofstructures 110 for thermally stressing the test subject 120 viaconduction heating and/or conduction cooling. In this embodiment,structures 110 are referred to as rails 110 and are illustrated ingreater detail in FIGS. 2 through 3D. Conduction heating and/orconduction cooling of the test subject 120 occurs by first heatingand/or cooling the rails 110, which then conduction heat and/orconduction cool the test subject 120. In one embodiment, the rails 110abut the edges of test subject 120, which allows the heating and/orcooling by conduction to take place.

Conduction cooling may take place, in one embodiment, by firstintroducing liquid nitrogen (LN₂) into a pipe 130; however, othercooling fluids may be utilized.

Previous HALT systems cooled and/or heated a test subject by convection,blowing cold and/or hot air over the test subject. Convection cooling,however, is not effective when testing a high-powered rail-cooled testsubject because convection cooling does not accurately simulate theenvironment that the test subject is exposed to in the field. Inparticular, certain temperature gradients that the test subject isexposed to in the field cannot be recreated in a test setting by blowingcold and/or hot air over the test subject. In contrast, thermal stresstesting of the test subject by conduction cooling and/or conductionheating more accurately simulates the environment that the test subjectis exposed to in the field. Additionally, cooling and/or heating byconduction, as opposed to convection, in one embodiment, maintains a drynitrogen atmosphere around the test subject, thereby eliminatingpotential electrical shorts due to moisture condensation.

Referring back to FIG. 1, the LN₂ flows through the pipe 130 and entersthe rails 110 through openings at the bottom of the rails 110. Afterentering the rails 110, the LN₂ flows throughout channels inside of therails 110, as is illustrated in, and described in greater detail inconjunction with, FIGS. 3C and 3D. As the LN₂ flows through the internalchannels of the rails 110, the LN₂ evaporates, thereby causing the rails110 to lose heat. Because the edges of test subject 120 abut the rails110, the heat loss experienced by the test subject 120 is transferred tothe rails 110, thereby conduction cooling the test subject 120. Afterthe LN₂ evaporates, the nitrogen gas exits the rails and vents acrossthe test subject 120. This process will be further described inconnection with FIG. 3A. It is noted that, in one embodiment, neitherthe LN₂ nor the nitrogen gas comes into contact with the electricalcomponents of the card. Conduction cooling the test subject 120 providesa benefit of more accurately emulating the thermal environment of thetest subject 120.

Conduction heating of the test subject 120 can take place by introducingone or more heated rods 172 into respective openings 112 in the rails110, as illustrated in FIG. 2. The rods 172 may include cartridgeheaters, or other types of heaters. Referring back to FIG. 1, power isprovided to the heated rods through a line 140. When powered, the heatedrods heat by conduction the rails 110. Because the edges of the testsubject 120 abut the rails 110, heat is transferred to the test subject120 through conduction.

Additionally, the testing apparatus 100 vibrationally stresses the testsubject 120. Vibrational stress is generated, in one embodiment, by oneor more pneumatic hammers 150 that are attached at one end 152 to thebottom of a base plate 180 upon which the rails 110 are fitted. Theother end of each pneumatic hammer 150 is left unattached so that it canimpart vibrations to the testing apparatus 100 when air is supplied tothe pneumatic hammers 150. The air that drives the pneumatic hammers 150may be supplied to the testing apparatus 100 via pipe 170. The testingapparatus 100 is fitted with shock mounts 160 between the base plate 180and the base 182 of the testing apparatus 100 for dampening thevibrations generated by the pneumatic hammers 150, in one embodiment.

In one embodiment of the invention, the testing apparatus 100 is housedinside of a chamber 184. Chamber 184 includes walls 186 that act assound proofing, dampening the sound generated by the testing apparatus100. Although one embodiment of the testing apparatus 100 utilizes achamber 184 as a housing, the testing apparatus 100 can be operatedwithout such a chamber 184, as can be seen in FIG. 2.

A computer 190 controls the test settings of the testing apparatus 100.Computer 190 controls the test settings of the testing apparatus 100 bytransmitting signals through a line 191 to an environment controller192. Environment controller 192, in turn, controls the heating, shaking,as well as cooling of the test subject 120 via control lines 194, 196,and 198 respectively. Computer 190 may also receive test results fromthe testing apparatus 100 while thermal and vibrational stresses areapplied to the test subject 120. Additional details of testconfiguration apparatus 100 are described in conjunction with FIGS. 2through 3D.

FIG. 2 is an illustration of selected portions of test configurationapparatus 100. The frame of the configuration apparatus 100 includesstructural support 183 and the base plate 180. In this embodiment, thetest subject 120 includes a plurality of circuit cards. The circuitcards are held in place by card guides 122, which can be seen moreclearly in FIG. 3A. The card guides 122 are also the location where therails 110 abut the test subject 120 and thus are the location whereconduction heating and/or conduction cooling of the test subject 120takes place.

With respect to conduction cooling, the LN₂ is piped into the rails 110through openings on the bottom of the rails 110. This will beillustrated more clearly in FIG. 3D. Once the LN₂ enters the rails 110,it flows through various circular channels emptying into centralchannels, which extend the entire height of the rails 110, in thisembodiment. This will be illustrated more clearly in FIG. 3C. Openings102 of the central channels are illustrated in FIG. 2 as the centeropenings in the top surface of the rails 110, which openings 102 areflanked on two sides by three openings 112 for receiving the heatedrods. From the central channels, the LN₂ flows into the cooling tubes,the openings 114 of which can be seen in FIG. 2. The cooling tubesextend the full length of the rails 110 and will be illustrated moreclearly in FIG. 3A. The cooling tubes are the location where the LN₂evaporates, thus conduction cooling the rails 110 and the card guides122 which conduction cool the test subject 120. Variable-sized plugs canbe inserted into the openings 114 of the cooling tubes, providing ameans for adjusting the amount of cooling of the test subject 120. Inone embodiment, because each opening 114 is associated with a specificcard guide 122, the temperature of each circuit card can be controlledindependently from the others.

FIG. 3A is an illustration of the inner face of the rail 110 of the testconfiguration apparatus. The rail 110 consists of the card guides 122into which the test subject is inserted. As mentioned in FIG. 2, thecard guides 122 are conduction cooled by evaporation of the LN₂ in thecooling tubes 113 within columns 115. Variable-sized plugs can beinserted into the openings 114 of the cooling tubes 113 in order tocontrol the amount of cooling of the test subject. Notches 124 in therail 110 are openings from which the nitrogen gas vents after coolingthe rail 110 and the card guides 122. With respect to conductionheating, the heated rods mentioned in connection with FIG. 1 can beinserted into the openings 112 to the heating tubes in the rail 110.

FIG. 3B is an illustration of an alternate view of the inner face of therail 110 of the test configuration apparatus.

The conduction cooling of the rails will be described in more detail inFIGS. 3C and 3D. FIG. 3C is a schematic diagram of a verticalcross-section of the short side of the rail 110.

FIG. 3D is a schematic diagram of a vertical cross-section of the longside of the rail 110. When thermally stressing the test subject byconduction cooling, LN₂ enters the rail 110 through slot 108. The LN₂ isthen circulated through the rail 110 via the circular channels 104 untilit reaches the opening 106 to the central channel 103. The LN₂ flowsinto the central channel 103, which then distributes the LN₂ to each ofthe vertical cooling tubes 113. As the LN₂ flows through the variouschannels, it evaporates, conduction cooling the rail 110 and card guides122, which conduction cools the test subject.

The teachings of the invention described hereinabove are applicable totesting purposes other than HALT, such as Highly Accelerated StressScreening (HASS).

Numerous other changes, substitutions, variations, alterations andmodifications may be ascertained by those skilled in the art and it isintended that the present invention encompass all such changes,substitutions, variations, alterations and modifications as fallingwithin the spirit and scope of the appended claims.

1. A testing apparatus for executing testing on at least one testsubject, comprising: a first set of channels for cooling the at leastone test subject by conduction, comprising: at least one first coolingchannel operable to receive a supply of liquid nitrogen and furtheroperable to distribute the supply of liquid nitrogen to at least onesecond cooling channel; the at least one second cooling channel,connected to the at least one first cooling channel, operable to receivethe supply of liquid nitrogen from the at least one first coolingchannel and further operable to distribute the supply of liquid nitrogento at least one third cooling channel; and the at least one thirdcooling channel, connected to the at least one second cooling channel,operable to receive the supply of liquid nitrogen from the at least onesecond cooling channel and further operable to cool by conduction astructure that is operable to cool by conduction the test subject; and asecond set of channels for heating the at least one test subject byconduction, comprising: at least one first heating channel operable toreceive at least one heating rod and further operable to heat byconduction a structure that is operable to heat by conduction the atleast one test subject.
 2. The testing apparatus of claim 1, wherein theat least one third cooling channel is at least substantiallyperpendicular to the at least one first heating channel.
 3. The testingapparatus of claim 1, wherein the at least one third cooling channelcomprises: vents operable to allow nitrogen gas to exit from the atleast one third cooling channel; and openings operable to regulate thecooling of the structure that is operable to cool by conduction the atleast one test subject.
 4. A testing apparatus for executing testing onat least one test subject, comprising: at least one structure operableto thermally stress the test subject via conduction; and at least onepneumatic hammer operable to input imparting vibrations to the testsubject.
 5. The testing apparatus of claim 4, and further comprising atleast one shock mount associated with the testing apparatus, the atleast one shock mount having vibration dampening capability.
 6. Thetesting apparatus of claim 4, wherein the at least one structure isoperable to thermally stress the test subject via conduction of heat tothe test subject.
 7. The testing apparatus of claim 4, wherein the atleast one structure is operable to thermally stress the test subject viaconduction cooling.
 8. The testing apparatus of claim 4, and furthercomprising the test subject, wherein the test subject is a circuit card.9. The testing apparatus of claim 4, wherein the at least one structureabuts the edges of the test subject.
 10. The testing apparatus of claim4, and further comprising a liquid nitrogen supply associated with theat least one structure; and a plurality of chambers formed in the atleast one structure and containing liquid nitrogen from the supply forcooling the test subject.
 11. The testing apparatus of claim 4, andfurther comprising heated rods disposed within the at least onestructure for thermally stressing the test subject via conduction.
 12. Amethod for executing testing of at least one test subject comprising:applying a thermal stress to the test subject via conduction at a rateof change of at least 8° C. per minute; and imparting vibrations to thetest subject at a rate of at least 3Gs rms.
 13. The method of claim 12,wherein applying a thermal stress comprises cooling the test subject byconduction.
 14. The method of claim 12, wherein applying a thermalstress comprises heating the test subject by conduction.
 15. The methodof claim 12, wherein the vibrations are imparted to the test subject byat least one pneumatic hammer.
 16. The method of claim 12, wherein thevibrations are dampened by at least one shock mount.
 17. The method ofclaim 12, wherein the test subject is a circuit card.
 18. The method ofclaim 12, wherein at least one structure for applying a thermal stressto the test subject via conduction abuts the edges of the test subject.19. The method of claim 13, wherein liquid nitrogen is used for coolingthe test subject by conduction.
 20. The method of claim 14, whereinheated rods are used for heating the test subject by conduction.